okay, i've asked my vet about this and he has very few ideas, he wants to check out the cats in person. i have a male and female cat, both spayed/neutered, brother and sister, about 2 years old. they have always gotten along great... they have their littler wrestling matches and like to stalk each other, like any cats do, but have never tried to hurt each other and always give each other space and respect.
now though, they cannot be in the same room. this started abruptly in the middle of the nite on friday and at this point they have to be constantly separated to avoid what i'd consider some pretty serious fighting. to make matters worse, the male is a lot bigger than the female so she takes the brunt of it.
both cats are extremely friendly and social, like always, with the rest of the family, they only have issues with each other... i guess i could understand if this was a gradual thing but it's literally like one day they're sleeping together, the next day they're snarling/yowling/bristling at the sight of one another. bascially one cat lives in our bedroom now...

any suggestions? anyone heard of this before? i don't want to have to get rid of one.